It's an abuse of power to do such things to any employee.
Most employees cave in because they need the job.
It's an employer's market when the workforce isn't majority unionized.
Collective bargaining - real collective bargaining & not the shonky employer placed representative agreeing with the boss in an enterprise agreement subversion - is the only thing that has, traditionally, helped a worker.
I don't know about your countries but unions certainly brought about the 8hr day, 4 weeks paid compulsory annual leave, a living wage, survivable working conditions, and safety for the public in Australia.
Employers, and the govt., are currently trying to wind those things back WHILST making record profits, paying dividends all over (Australia is dividend heaven) and making record payments to board members + CEOs etc.